The conventional coal separation is mainly wet processing in which medium is water. The wet processing method causes much water consumption and high investment and serious environmental pollution. In addition, coal separation is difficult with this method in arid areas.
The U.S. Pat. No. 4,194,971 and China Patent No. CN87101056A have disclosed respectively a dry separation apparatus with fluidized bed. The U.S. Pat. No. 4,194,971 is based on the principle of chemical engineering reactor. The particulate material forms a fluidized bed in an elongated, horizontally extending container, and the moveable scrapers are arranged inside the container. The endless motion of the scrapers compels the lighter material floating on the upper portion of the bed to move and to concentrate to one end, while the heavier material to the other end according to the principle of chemical engineering reactor. So the materials are separated. In the separation process the heavy medium fed into the bed is removed from the bed along with the heavier material. The main disadvantages of this kind of apparatus are:
1. The separation apparatus designed according to the principle of chemical engineering reactor can not meet the needs of industrial applications, as the float on the upper bed layer is scrapped out by the scrapers while the sink is removed by flowing on its own, which limits the handling capacity of the apparatus seriously.
2. The material is fed from the top middle of the bed and lighter and heavier material move in counter-current, which greatly reduces the stability of the fluidized bed and separation precision.
3. The apparatus uses scrapers without holes to scrape the float on the upper bed layer, which not only makes the upper portion of the bed disturbed seriously, but also limits the height and the velocity of the scraper. Therefore, the separation precision and the capacity are reduced.
4. The heavy medium is removed and recovered outside the bed, which makes it very difficult to run the apparatus continuously under certain special conditions.
It's known from China Patent No. CN 87101056A "Coal Dry Cleaning Method and Apparatus with Fluidized Bed" that the apparatus which separates materials on their different densities is mainly composed of the output system with anchorchain-scraper, the medium recovering device, the housing of the fluidized bed and the air distributor. The raw coal fed by the feeder stratifies according to the density in the fluidized bed which is formed by mixed air and fine particulate material with a certain uniformly distributed density and then the anchorchain-scrapers immersed in the bed scrape the lighter material i.e. the float and the heavier material i.e. the sink towards the two ends of the bed respectively to realize the separation. In this patent the raw coal and the heavy medium are fed from the top to the middle part of the separation section, which reduces the stability of the middle portion of the fluidized bed, the length of the separation section and the effective period of separation, and the separation precision is also greatly decreased. Anchorchain-scraper output system is immersed entirely in the fluidized bed, which limits the height of the scraper and the handling capacity of the separator. If the moving velocity of scraper exceeds a limit value, the stability and the homogeneity of fluidized bed will be destroyed, which will result in the chaos of the fluidized bed. So the clean coal and the waste rock in the separation section will confuse each other. Therefore the separation precision will be reduced. In addition, in the anchorchain-scraper output system, holeless single chain boards with reinforced ribs are used, which makes coal and waste rock mixed up on the ribs. Linked with ring chains, the scrapers are liable to sink and touch the air distributor, which makes the distributor easily damaged. The factors mentioned above result in the disadvantages of the apparatus such as low separation precision and capacity, etc.
The aim of this invention is to overcome the disadvantages existing in the prior art separation apparatus with the fluidized bed mentioned above and to improve the separation precision and the capacity to meet the needs of industrial applications.